Typical laundry prespotting compositions that are aqueous-based are designed to remove various water-borne stains, including grape juice, mustard, grass, chocolate, clay, and similar stains. Such formulations can lack effectiveness in removing oil-borne stains, including stains from cooking oil, fat, spaghetti sauce, sebum, grease, motor oil, and the like.
One highly successful commercial aqueous laundry prespotting composition that has been marketed as LIQUID SHOUT.RTM. is described in U.S. Pat. No. 4,595,527, issued Jun. 17, 1986. This composition exhibits precleaning properties for both oil and water-borne stains. The composition includes, among other things, effective amounts of a chelating agent, a nonionic surfactant, and water. The use of enzymes is not expressly precluded but also is not suggested.
It is known that the introduction of enzymes in heavy duty liquid detergents helps improve the wash performance of these products for certain stains. Thus, proteases improve the removal of protein-based stains, such as blood, egg, and grass stains. Amylase improves the wash efficiency for starch stains, such as those caused by gravy. Lipases are effective in removing triglyceride-based stains, such as cooking oil, fat, and sebum stains and the like.
However, there are inherent problems with employing cleaning compositions containing enzymes. When an enzyme is added to an aqueous medium without steps taken to stabilize the enzyme, the enzyme typically is rapidly denatured in the water. Consequently, a loss of enzyme activity is observed over time. Accordingly, in order to provide commercially practical aqueous enzyme detergent compositions, the art has found it necessary to stabilize the enzymes so that they retain their activity for long periods of shelf-storage time.
Many means and formulations have been proposed to stabilize enzymes present in water-based compositions. For example, in U.S. Pat. No. 4,243,546, issued Jan. 6, 1981, a stabilizing system for an enzyme is disclosed that includes an alkanolamine and an acid. In U.S. Pat. No. 4,318,818, issued Mar. 9, 1982, it is disclosed that a calcium salt, a short chain carboxylic acid such as a formate, and an alcohol can be employed to stabilize an aqueous enzyme composition. It is of interest to note that in the '818 patent, column 7, lines 20-23, it is stated that the enzyme-containing composition must be substantially free of sequestrants, such as polyacids and chelating agents. Such sequestrants in amounts over about 1% by weight are identified as undesired, since they remove enzyme-stabilizing calcium from the composition by forming calcium complexes.
In U.S. Pat. No. 4,404,115, issued Sep. 13, 1983, it is proposed to employ a boron-containing enzyme stabilizer, such as an alkali metal borate, in the enzymatic aqueous cleaning compositions of the patent. It is also disclosed that other stabilizers, such as an alkali metal sulphite and/or a polyol, preferably also are present. The '115 patent also teaches use of builders, such as tripolyphosphates, EDTA, citrates and the like. However, the patent also discloses that when such builders were employed in the absence of a borate stabilizer, comparative tests showed that there was no enzyme activity remaining after only two weeks storage at elevated temperatures. Similar results are illustrated in U.S. Pat. No. 4,462,922, issued Jul. 31, 1984. Thus, these patents teach that enzymes are stable in the presence of the chelating builders disclosed only if the borate enzyme stabilizer also was present.
In Novo's Handbook of Practical Biotechnology, 2nd Edition, pp. 54-57, published by Novo Industri A/S (Denmark) in 1986, it is disclosed that enzyme stability is enhanced by the presence of calcium, alcohols, and other stabilizers. It is also disclosed that builders (generally metal-chelating agents) bind ions such as calcium and effectively remove them from solution. Sodium citrate is referred to as an example of such a compound. The Novo Handbook states that such builders or chelating agents destabilize enzymes. In addition, on pages 55 and 56, the Novo Handbook recommends that in order to obtain good enzyme stability, the water level of the product should not be too high. A water level of 55% by weight or less is recommended. In Novo's U.S. Pat. No. 5,156,773, issued Oct. 20, 1992, it is also taught that the presence of detergent builders reduces the storage stability of liquid enzymatic detergents.
From these examples, it is seen that the clear expectation of the art has been that chelating agents destabilize enzymes and must not be used except in very small amounts in the absence of enzyme stabilizing systems. However, in direct opposition to this restriction on the use of chelating agents, it is considered otherwise desirable for cleaning purposes to employ chelating agents as builders in laundry cleaning compositions to assist in controlling mineral hardness and to enhance the surfactancy of nonionic detergents contained in the compositions. This is a basic conflict in needs, and the various and generally multi-ingredient enzyme stabilizing formulations of the art are intended to address this conflict.
However, the need to employ extra enzyme stabilizing ingredients has important practical disadvantages in that it adds to the cost of enzyme-containing laundry cleaning compositions in an industry in which even small incremental increases in production costs can cause a formulation not to be competitive in the marketplace. It is therefore desirable to create an enzyme laundry cleaning composition that includes a chelating agent but that is substantially free of enzymatic stabilizers beyond a specific, limited enzymatic stabilization system, in order to obtain the enzyme stain removal and other cleaning advantages of the formulation but also to reduce cost and maintain market competitiveness by omitting the use of avoidable ingredients.